MCC EPICS Knobs

Sonya Hoobler

25 July 2008

Background Knobs are another way to adjust control system

variables (like slider or text entry) User ‘attaches’ device to knob, turns knob, device

value is changed SLC knobs:

Motivation: move away from Alpha and Knobs PC, control EPICS devices

...SCP knob software

knob control software

MCC Alpha Knobs PC

OPI (SCP COW)

OPI (SCP COW)

Knob Box

Knob Box

to devices

via SLC micros

RS-485ethernet

Background Continued: SCP Knobs

User Interface (two examples)

Knob Box

•Rack-mounted chassis, 4 knobs per box

•Each knob has: 16-character, 11-segment LED display and on/off button; incremental shaft encoder used to count turns and store value in buffer

•Uses RS-485 serial protocol

• Responds to requests for turns count

•Prints message on LED display in response to commands •Only designated devices could be assigned to a

knob

•Functions: change knob gain, restore knob

EPICS Knobs

Same knob boxes One soft IOC per knob box

Use Streamdevice to communicate with knob box Polls knob box for turns count Sends legend updates to knob box

When user ‘attaches’ a PV, the PV name is copied to the .INP of an ai record and the .OUT field of an ao record

Similarly, the PV.EGU, .DRVH, .DRVL, .DESC field values are fetched

to devices

via EPICS IOCs

performs function of SCP knob software + knob control

Soft IOC running on lcls-daemon

Terminal Server

RS-485ethernet

LCLS OPI

Knob Box

User Interface Launch GUI from LCLS OPI taskbar

User Interface (continued)

Current value of device

Value saved by user

Value when device was attached

Store Value in Saved

Load Saved Value

Load Initial Value (restore)

Knob sensitivity in units/turn

Knob state: attaching, attached, detaching, detached Detach knob

PV name: middle-click drag-and-drop or type name and hit Enter

User interface (continued)

Miscellaneous Must use BCTRL (perturb) PV to control

magnets. (Using BDES would require sending ‘trim’ command.)

Software will allow user to attach any PV, doesn’t recognize those that can be adjusted.

Software generates device description for legend (only 9 characters available). Would be nice to have a general way to do this for all commonly-used EPICS PVs.

Software also generates knob sensitivity. Uses DRVH and DRVL, if defined.